Vapor electric device



bet. 6, 1942. J. H. COX

VAPOR ELECTRIC DEVICE Filed Aug. 5, 1940 m ht iNVENTOR Joseph H, Cox

J. 4. JW

ATTORNEY WITNESSES: 92141 m Patented Oct. 6, 1942 VAPOR ELECTRIC DEVICE Joseph H. Cox, Forest Hills, Pa., assignor to Westingliouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 3, 1940, Serial No. 350,224.

2 Claims.

My invention relates to a vapor-electric device, and particularly to a control system for securing reliable initiation of the main arc in the valves of a make-alive type converter.

In the operation of a make-alive type converter difficulty has heretofore been experienced because of the non-firing of certain valves of the converter, that is, the occasional failure of a make-alive type element to maintain the cathode spot for a suflicient interval to establish a main current carrying arc in the valve.

Also, on the so-called anode firing systems difficulty has been experienced because of the destruction of the control tubes by follow current, or power current, as the result of failure of the main anode pick up.

It has heretofore been proposed to remedy this situation by a so-called condenser firing system in which a condenser is charged by a surge or impulse of unidirectional current and the condenser discharged through a suitable control tube to supply a starting impulse or cathode initiating impulse to the make-alive electrode.

According to my invention, the disadvantage of these prior systems has been eliminated by charging the capacitor from a suitable alternating current source through a suitable impedance and discharging the capacitor at or near the peak of the charging potential, so that the condenser discharge produces the necessary makealive impulse to establish the cathode spot, and the potential'of the charging means provides an exciting current which maintains the cathode spot for a suflicient time interval to insure pick up of the main arc in a converter.

My system has the further advantage in that the make-alive current flows only in a local exciting circuit and is kept free of the load on the main transformer so that variations in the amount of the load or even the total disconnection of the load, will not affect the control.

scription taken in coniunction with the accompanying drawing, in which:

Figure 1 is a schematic illustration of a vapor electric device embodying my invention;

Fig. 2 is a diagrammatic illustration of the potentials and current in the charging transformer; and

Fig; 3 is a diagrammatic illustration of a combined make-alive excitation current flowing in the make-alive electrode. In the illustrated embodiment of my invention according to Fig. i, an alternating current circuit i is connected to a direct current circuit 2 by means of a suitable rectifier transformer 3 and a plurality of make-alive type valves 4 for determining the current conveyed between the alternating current circuit i and the direct current circuit 2. Each of the make-alive type valves 4 comprises a main anode 5, a vaporizable main cathode 6 and a make-alive electrode 1 for periodically initiating a cathode spot on the cathode G.

The control system for supplying make-alive and excitation current to the make-alive electrodes 1 comprises a charging transformer 8 which is connected to suitable capacitors 9 through impedances ill for controlling the rate of current flow to the capacitors 9. The capacitors 9 are, in turn connected to the anodes ll of suitable grid controlled firing tubes i2 by means of relatively low impedances l3 so that the flow of charging current to the capacitors 9 covers a considerable interval of time and so that the discharge of the capacitor energy may be accomplished in a relatively short time.

A suitable grid transformer I4 is provided for controlling the grids ii of the firing tubes I2 and the instant of application of the control potential through the grid is controlled by means of a suitable phase shifting device herein illustratedas a so-called induction phase shifter l6.

Preferably the charging transformer 8 is so phased with respect to the rectifier transformer 3 that the capacitors 9 are substantially fully charged at the instant of discharge to initiate the cathode spot and the phase winding of the charging transformer associated therewith is near its peak potential.

Both the charging and discharging impedances are of such value that after the termination or the discharge from the capacitor 9, exciting current of suitable value will flow through the impedances I II and I3 and the firing tube I! to maintain a keep-alive are from a holder of the make-alive electrode 1.

I have found that with a potential of from 150 to 200 volts at the terminals of the charging transformer 8 and a capacitor 9 of approximately 20 microfarads that the charging impedance in may have a value of from 30 to115 ohms, while the discharging impedance [3 may operate satisfactorily with an impedance of the order of I claim as my invention: l. A control system for a make-alive type converter comprising a plurality of make-alive valves, a make-alive electrode for each valve'of the converter, a charging transformer having phase windings for each valve of the converter, a capacitor connected to each phase terminal of the transformer to be ,charged therefrom, an impedance of the order of from 30 to 115 ohms connected between said phase terminals and the respective capacitors, an auxiliary controlled valve in series with each of said make-alive elecciated make-alive electrodes I to successively and periodically initiate curent flow in the make-alive type valves 4.

The current flow from the charging transformer 8 to the capacitors 9,0ccursover a rela-.

capacitor 9 discharges through the make-alive electrode 1 to produce an impulse 20 of current having a very steep wave front and extending over a very short'interval of time T2.

However, as the potential of the charging transformer winding 8 is still material, current will continue to flow through the impedances l0 and I3 and the firing tube l2 to the make-alive electrode 1, and because of the impedance of the make-alive electrode 1, an exciting arc will be established from th make-alive electrode holder to maintain the cathode spot for an interval of Ta.

The combined make-alive excitation impulse produces an excitation wave having a very steep high current front and a relatively fiat low current trailing portion for reliably initiating the main current carrying arc in the make-alive valves.

While for purpose of illustration I have shown and described a specific embodiment of my invention, it will be apparent that changes and modifications can be made therein without departing from the true spirit of my invention or the scope of the appended claims.

capacitors and the respective make-alive electrodes, means for energizing said auxiliary valves to periodically and successively discharge said capacitors through the respective make-alive electrodes, said charging transformer being so phased that at the instant of discharge of the capacitors sufiicient potential remains to supply exciting current through said impedances to the make-alive electrodes.

2. A control system for a multi-valve makealive type converter comprising a make-alive electrode for each valve of the converter, a source of control potential having phase terminals for each valve of the converter, a capacitor connected to each phase terminal of the transformer to be charged therefrom, an impedance of the order of from 30 to ohms connected between said phase terminals and the respective capacitors, an auxiliary controlled valve in series with each oflsaid make-alive electrodes, control means for energizing said auxiliary valves to periodically and successively discharge said capacitors through the respective make-alive electrodes, a resistance of the order of 5 ohms connected in series with each of said make-alive electrodes, said control transformer and said charging transformer being so 'rvlated in phase position that the charging transformer supplies an exciting current through said impedance and said resistor to the make-alive electrodes for a material interval after the discharge of said capacitor.

JOSEPH H. COX. 

